1. Field of the Invention
The present invention relates to a power transmission control apparatus for a vehicle.
2. Description of the Related Art
As described in, for example, Japanese Patent Application Laid-Open (kokai) No. 2010-48416, there has been known a transmission which includes first and second input shafts for receiving power from an engine of a vehicle; an output shaft for outputting power to drive wheels of the vehicle; a first mechanism section which selectively establishes any one of some (odd gears including first gear) of all the gears to thereby form a power transmission system between the first input shaft and the output shaft; and a second mechanism section which selectively establishes any one of the remaining gears (even gears including second gear) to thereby form a power transmission system between the second input shaft and the output shaft.
This transmission includes first and second clutches in combination. The first clutch selectively achieves an engaged state so as to form a power transmission system between the output shaft of the engine and the first input shaft, or a disengaged state so as to cut off the power transmission system. The second clutch selectively achieves an engaged state so as to form a power transmission system between the output shaft of the engine and the second input shaft, or a disengaged state so as to cut off the power transmission system. A mechanism obtained through such a combination is called a “double clutch transmission (hereinafter also referred to as “DCT”). The first and second clutches are configured such that, by means of adjusting clutch stroke in an engaged state, the transmittable maximum torque (clutch torque) can be adjusted. In the following description, the system constituted by the first clutch, the first input shaft, and the first mechanism section will be referred to as the “first system,” and the system constituted by the second clutch, the second input shaft, and the second mechanism section will be referred to as the “second system.” An engaged state of each clutch in which slippage is involved will be referred to as a “half-engaged state,” and an engaged state of each clutch in which no slippage is involved will be referred to as a “full-engaged state.”
When the DCT is controlled, one gear to be achieved (hereinafter referred to as the “selected gear”) is selected on the basis of a movement of a shift lever by a driver of the vehicle and/or travelling conditions of the vehicle. In the following description, of the first and second mechanism sections, the first and second clutches, the first and second input shafts, and the first and second systems, those corresponding to the selected gear will be referred to as the “selected mechanism section,” the “selected clutch,” the “selected input shaft,” and the “selected system”; and those not corresponding to the selected gear will be referred to as the “unselected mechanism section,” the “unselected clutch,” the “unselected input shaft,” and the “unselected system.”
When a gear is selected, the selected clutch is controlled into an engaged state in a state in which the selected gear is established in the selected mechanism section, and the unselected clutch is controlled into a disengaged state. As a result, a power transmission system which has a speed reduction ratio for the selected gear is formed between the output shaft of the engine and the output shaft of the transmission via the selected system. Drive torque (engine torque) of the engine is transmitted to the drive wheels via the power transmission system, whereby the vehicle can be accelerated.
Meanwhile, in the unselected system, the unselected clutch is in a disengaged state. Accordingly, the unselected mechanism section can be caused to wait in a state in which a gear which is selected (may be selected) next is established. By making use of this, the following operation is enabled. Even in the case where a gear shift operation (upshift to a higher gear or downshift to a lower gear) results in reciprocal switching of the states of the first and second systems between the selected and unselected states, the engine torque can be continuously transmitted, without interruption, to the output shaft of the transmission (accordingly, to the drive wheels), through simultaneous execution of an “operation of bringing the engaged one of the first and second clutches into a disengaged state” and an “operation of bringing the disengaged one of the first and second clutches into an engaged state.” As a result, gear shift shock can be reduced.